1. Field of The Invention
The present invention generally relates to microfabrication techniques and, in particular, to a microfabricated electromagnetic system and a method for forming electromagnets integrated within microfabricated devices.
2. Related Art
As known in the art, microfabrication processes are utilized to construct small, low profile devices that can be batch fabricated at a relatively low cost. In this regard, multiple devices are typically manufactured on a single wafer during microfabrication. Well known microfabrication techniques are used to form similar components of the multiple devices during the same manufacturing steps, and once the multiple devices have been formed, they can be separated into individual devices. Examples of microfabrication techniques that allow the batch fabrication of multiple devices are, but are not limited to, techniques commonly used in integrated circuit fabrication (e.g., diffusion, implantation, oxidation, chemical vapor deposition, sputtering, evaporation, wet and dry etching, etc.), electroforming (e.g., electroplating, electrowinning, electrodeposition, etc.), packaging techniques (e.g., lamination, screen printing, etc.), photolithography, and thick or thin film fabrication techniques. Since a large number of devices can be formed by the same microfabrication steps, the costs of producing a large number of devices through microfabrication techniques are less than the costs of serially producing the devices through other conventional techniques. Accordingly, it is desirable, in most applications, to fabricate devices through microfabrication techniques.
In many applications, it is also desirable for the devices to include an electromagnet in order to actuate certain features of the device or to perform other functionality. Furthermore, as known in the art, the strength of an electromagnetic flux may be increased by increasing the number of turns of the electromagnet""s coil. Therefore, many conventional designs for electromagnets wind the coils around magnetic material through multiple turns in order to generate a sufficient electromagnetic flux for a particular application.
As known in the art, winding the coils concentrically around the magnetic material in the same plane can cause leakage losses. This is because the amount of flux concentrated in the magnetic material of the electromagnet is decreased as the electromagnet""s coil is positioned further from the magnetic material of the electromagnet. In order to keep the electromagnet""s coils close to the magnetic material for minimizing leakage losses, most conventional designs for electromagnets spiral the coil around the magnetic material in a non-planar fashion until the number of desired turns is reached.
However, conventional non-planar windings are difficult to achieve through conventional microfabrication techniques. As a result, most conventional devices have coils that are not batch fabricated through microfabrication techniques. Instead, the coils for each electromagnet are usually formed individually by mechanically wrapping the coils around magnetic material or by other techniques that individually form the coils of each electromagnet. Accordingly, the costs of manufacturing the electromagnets are increased since the benefits of batch fabrication are not utilized in forming the coils of the electromagnets.
Another problem increasing the difficulty of microfabricating efficient electromagnets is flux saturation. As known in the art, magnetic material has a flux density that limits the amount of flux that a given cross-sectional area of magnetic material can carry. Therefore, when the area of magnetic material for a conventional electromagnet is reduced to a microfabricated scale, the amount of flux capable of being carried by the magnetic material is also reduced. As a result, many conventional designs for electromagnets are inadequate for producing a sufficient electromagnetic flux at a microfabricated scale.
Thus, a heretofore unaddressed need exists in the industry for providing a system and method of efficiently microfabricating an electromagnet and for reducing the effects associated with flux saturation, and leakage.
The present invention overcomes the inadequacies and deficiencies of the prior art as discussed herein. In general, the present invention provides a system and method for efficiently integrating electromagnets within microfabricated devices.
The present invention includes a magnetic core having a plurality of cavities. A conductive coil is passed through the cavities and around portions of the magnetic core between the cavities. When electrical current is passed through the conductive coil, an electromagnetic flux is generated which flows through the magnetic core. Since the coil is passed around various portions of the magnetic core, the electromagnetic flux is distributed, thereby minimizing leakage losses and saturation problems associated with manufacturing electromagnets at microfabricated levels.
In accordance with another feature of the present invention, each segment of the conductive coil is planar. Therefore, the conductive coil can be easily manufactured via microfabrication techniques. When the conductive coil is formed on different layers of a microfabricated device, vias can be formed in the layers. The different portions of the conductive coil can be interconnected through these vias, thereby preserving the conductive coil""s compatibility with microfabrication techniques.
In accordance with another feature of the present invention, a movable member of magnetic material is positioned close to the magnetic material of the electromagnet. The electromagnetic flux can be distributed along the surface of the movable member in order to generate a plurality of relatively small forces acting on the movable member. This plurality of small forces add together in order to induce the movable member to move, while avoiding magnetic saturation.
In accordance with another feature of the present invention, portions of the conductive coil are coupled directly to the magnetic core, a portion of which is electrically conducting and which acts to electrically interconnect coil segments. Therefore, different segments of the conductive coil can be formed on different layers of a microfabricated device without having to directly interconnect the segments of the conductive coil, thus facilitating fabrication.
In accordance with another feature of the present invention, permanent magnetic material is incorporated into the magnetic circuit of the electromagnet and induces a permanent magnetic flux that can either reinforce or counteract the electromagnetic flux flowing through the magnetic core.
The present invention has many advantages, a few of which are delineated hereafter, as mere examples.
An advantage of the present invention is that electromagnets can be easily and efficiently integrated into microfabricated devices.
Another advantage of the present invention is that leakage loss and saturation problems can be minimized when an electromagnet is manufactured at microfabrication levels.
Another advantage of the present invention is that the effects of reluctance and eddy current loss can be reduced.
Another advantage of the present invention is that batch fabrication of microfabricated devices having electromagnets is facilitated.
Another advantage of the present invention is that the conductive coil of the electromagnet can be fully formed through microfabrication techniques.
Other features and advantages of the present invention will become apparent to one skilled in the art upon examination of the following detailed description, when read in conjunction with the accompanying drawings. It is intended that all such features and advantages be included herein within the scope of the present invention, as is defined by the claims.